[RFC PATCH v2 5/5] target/arm/cpu: Add the kvm-no-adjvtime CPU property

[Andrew Jones]

kvm-no-adjvtime is a KVM specific CPU property and a first of its kind.
To accommodate it we also add kvm_arm_add_vcpu_properties() and a
KVM specific CPU properties description to the CPU features document.

Signed-off-by: Andrew Jones <address@hidden>
---
 docs/arm-cpu-features.rst | 31 ++++++++++++++++++++++++++++++-
 hw/arm/virt.c             |  8 ++++++++
 include/hw/arm/virt.h     |  1 +
 target/arm/cpu.c          |  2 ++
 target/arm/cpu64.c        |  1 +
 target/arm/kvm.c          | 28 ++++++++++++++++++++++++++++
 target/arm/kvm_arm.h      | 11 +++++++++++
 target/arm/monitor.c      |  1 +
 tests/arm-cpu-features.c  |  4 ++++
 9 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/docs/arm-cpu-features.rst b/docs/arm-cpu-features.rst
index 1b367e22e16e..641ec9cb8f4a 100644
--- a/docs/arm-cpu-features.rst
+++ b/docs/arm-cpu-features.rst
@@ -31,7 +31,9 @@ supporting the feature or only supporting the feature under 
certain
 configurations.  For example, the `aarch64` CPU feature, which, when
 disabled, enables the optional AArch32 CPU feature, is only supported
 when using the KVM accelerator and when running on a host CPU type that
-supports the feature.
+supports the feature.  While `aarch64` currently only works with KVM,
+it could work with TCG.  CPU features that are specific to KVM are
+prefixed with "kvm-" and are described in "KVM VCPU Features".
 
 CPU Feature Probing
 ===================
@@ -171,6 +173,33 @@ disabling many SVE vector lengths would be quite verbose, 
the `sve<N>` CPU
 properties have special semantics (see "SVE CPU Property Parsing
 Semantics").
 
+KVM VCPU Features
+=================
+
+KVM VCPU features are CPU features that are specific to KVM, such as
+paravirt features or features that enable CPU virtualization extensions.
+The features' CPU properties are only available when KVM is enabled and
+are named with the prefix "kvm-".  KVM VCPU features may be probed,
+enabled, and disabled in the same way as other CPU features.  Below is the
+list of KVM VCPU features and their descriptions.
+
+  kvm-no-adjvtime          When disabled, each time the VM transitions
+                           back to running state from the paused state the
+                           VCPU's vitual counter is updated to ensure the
+                           stopped time is not counted.  This avoids time
+                           jumps surprising guest OSes and applications,
+                           as long as they use the virtual counter for
+                           timekeeping, but has the side effect of the
+                           virtual and physical counters diverging.  All
+                           timekeeping based on the virtual counter will
+                           appear to lag behind any timekeeping that does
+                           not subtract VM stopped time.  The guest may
+                           resynchronize its virtual counter with other
+                           time sources as needed.  Enabling this KVM VCPU
+                           feature provides the legacy behavior, which is
+                           to also count stopped time with the virtual
+                           counter.
+
 SVE CPU Properties
 ==================
 
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index cb7041e9677a..e9a08eb883bf 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1664,6 +1664,11 @@ static void machvirt_init(MachineState *machine)
             }
         }
 
+        if (vmc->kvm_no_adjvtime &&
+            object_property_find(cpuobj, "kvm-no-adjvtime", NULL)) {
+            object_property_set_bool(cpuobj, true, "kvm-no-adjvtime", NULL);
+        }
+
         if (vmc->no_pmu && object_property_find(cpuobj, "pmu", NULL)) {
             object_property_set_bool(cpuobj, false, "pmu", NULL);
         }
@@ -2154,8 +2159,11 @@ DEFINE_VIRT_MACHINE_AS_LATEST(5, 0)
 
 static void virt_machine_4_2_options(MachineClass *mc)
 {
+    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
+
     virt_machine_5_0_options(mc);
     compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
+    vmc->kvm_no_adjvtime = true;
 }
 DEFINE_VIRT_MACHINE(4, 2)
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 0b41083e9d5c..80e00161b8f2 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -109,6 +109,7 @@ typedef struct {
     bool smbios_old_sys_ver;
     bool no_highmem_ecam;
     bool no_ged;   /* Machines < 4.2 has no support for ACPI GED device */
+    bool kvm_no_adjvtime;
 } VirtMachineClass;
 
 typedef struct {
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 7a4ac9339bf9..53c73c25a67f 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -2482,6 +2482,7 @@ static void arm_max_initfn(Object *obj)
 
     if (kvm_enabled()) {
         kvm_arm_set_cpu_features_from_host(cpu);
+        kvm_arm_add_vcpu_properties(obj);
     } else {
         cortex_a15_initfn(obj);
 
@@ -2673,6 +2674,7 @@ static void arm_host_initfn(Object *obj)
     if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
         aarch64_add_sve_properties(obj);
     }
+    kvm_arm_add_vcpu_properties(obj);
     arm_cpu_post_init(obj);
 }
 
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index a39d6fcea34f..3cd416db8089 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -605,6 +605,7 @@ static void aarch64_max_initfn(Object *obj)
 
     if (kvm_enabled()) {
         kvm_arm_set_cpu_features_from_host(cpu);
+        kvm_arm_add_vcpu_properties(obj);
     } else {
         uint64_t t;
         uint32_t u;
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index a55fe7d7aefd..7666b250ab96 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -17,6 +17,8 @@
 #include "qemu/timer.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
+#include "qom/object.h"
+#include "qapi/error.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/kvm.h"
 #include "sysemu/kvm_int.h"
@@ -179,6 +181,32 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     env->features = arm_host_cpu_features.features;
 }
 
+static bool kvm_no_adjvtime_get(Object *obj, Error **errp)
+{
+    return !ARM_CPU(obj)->kvm_adjvtime;
+}
+
+static void kvm_no_adjvtime_set(Object *obj, bool value, Error **errp)
+{
+    ARM_CPU(obj)->kvm_adjvtime = !value;
+}
+
+/* KVM VCPU properties should be prefixed with "kvm-". */
+void kvm_arm_add_vcpu_properties(Object *obj)
+{
+    if (!kvm_enabled()) {
+        return;
+    }
+
+    ARM_CPU(obj)->kvm_adjvtime = true;
+    object_property_add_bool(obj, "kvm-no-adjvtime", kvm_no_adjvtime_get,
+                             kvm_no_adjvtime_set, &error_abort);
+    object_property_set_description(obj, "kvm-no-adjvtime",
+                                    "Set on to disable the adjustment of "
+                                    "the virtual counter. VM stopped time "
+                                    "will be counted.", &error_abort);
+}
+
 bool kvm_arm_pmu_supported(CPUState *cpu)
 {
     KVMState *s = KVM_STATE(current_machine->accelerator);
diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index 16b53e45377d..7d76f26beaca 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -232,6 +232,15 @@ void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map);
  */
 void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
 
+/**
+ * void kvm_arm_add_vcpu_properties:
+ * @obj: The CPU object to add the properties to
+ *
+ * Add all KVM specific CPU properties to the CPU object. These
+ * are the CPU properties with "kvm-" prefixed names.
+ */
+void kvm_arm_add_vcpu_properties(Object *obj);
+
 /**
  * void kvm_arm_get_virtual_time:
  * @cs: CPUState
@@ -319,6 +328,8 @@ static inline void 
kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     cpu->host_cpu_probe_failed = true;
 }
 
+static inline void kvm_arm_add_vcpu_properties(Object *obj) {}
+
 static inline bool kvm_arm_aarch32_supported(CPUState *cs)
 {
     return false;
diff --git a/target/arm/monitor.c b/target/arm/monitor.c
index fa054f8a369c..9725dfff16d4 100644
--- a/target/arm/monitor.c
+++ b/target/arm/monitor.c
@@ -103,6 +103,7 @@ static const char *cpu_model_advertised_features[] = {
     "sve128", "sve256", "sve384", "sve512",
     "sve640", "sve768", "sve896", "sve1024", "sve1152", "sve1280",
     "sve1408", "sve1536", "sve1664", "sve1792", "sve1920", "sve2048",
+    "kvm-no-adjvtime",
     NULL
 };
 
diff --git a/tests/arm-cpu-features.c b/tests/arm-cpu-features.c
index 06ed05e934e6..738e49447377 100644
--- a/tests/arm-cpu-features.c
+++ b/tests/arm-cpu-features.c
@@ -435,6 +435,8 @@ static void test_query_cpu_model_expansion(const void *data)
     assert_has_feature_enabled(qts, "cortex-a15", "pmu");
     assert_has_not_feature(qts, "cortex-a15", "aarch64");
 
+    assert_has_not_feature(qts, "max", "kvm-no-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         assert_has_feature_enabled(qts, "max", "aarch64");
         assert_has_feature_enabled(qts, "max", "sve");
@@ -469,6 +471,8 @@ static void test_query_cpu_model_expansion_kvm(const void 
*data)
         return;
     }
 
+    assert_has_feature_disabled(qts, "host", "kvm-no-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         bool kvm_supports_sve;
         char max_name[8], name[8];
-- 
2.21.0